1. Field of the Invention
The present invention relates to thin-film magnetic heads mounted in, for example, hard disk drives. Specifically, the present invention relates to a thin-film magnetic head and to a method that is capable of production of the thin-film magnetic head having a highly precise planar shape.
2. Description of the Related Art
FIG. 5 is an enlarged cross-sectional view away from a recording medium of a conventional thin-film magnetic head. This thin-film magnetic head is a reading head using magnetoresistive effects, and is provided at the side face, lying at the trailing edge, of a slider of a floating head. An inductive magnetic head for writing may also be disposed on the reading head.
A lower shielding layer 1 is formed of an alloy, e.g. sendust or permalloy (a Nixe2x80x94Fe alloy). A lower gap layer 2 composed of a nonmagnetic material, e.g. alumina (Al2O3), is formed on the lower shielding layer 1, and a magnetoresistive layer 15 is deposited thereon. The magnetoresistive layer 15 comprises a giant magnetoresistive (GMR) element, such as an anisotropic magnetoresistive (AMR) element or a spin-valve film. The magnetoresistive layer 15 senses leakage magnetic fluxes from a recording medium as a change in resistance and outputs them as a change in voltage. The magnetoresistive layer 15 has a width T4 in the direction of the track width (the transverse direction in the drawing), and the width T4 is slightly larger than the track width Tw.
Hard magnetic bias layers 4 are formed as a longitudinal bias layer at both sides of the magnetoresistive layer 15, and electrode layers 5 that are composed of an electrically conductive nonmagnetic material, such as chromium or tantalum are formed on the hard magnetic bias layers 4. An upper gap layer 7 composed of a nonmagnetic material such as alumina is formed on the electrode layers 5, and an upper shielding layer 8 composed of, for example, permalloy is formed on the upper gap layer 7.
A method for making the magnetoresistive layer 15 shown in FIG. 5 will now be described with reference to FIGS. 6A to 6C and 7A to 7B. The drawings at the left sides and the right sides of FIG. 6A to 6C and FIGS. 7A to 7B are cross-sectional views and plan views, respectively, of the thin-film magnetic head in each production step. The cross-sectional view shown in FIG. 6A is taken from a transverse line at the central region of the magnetoresistive layer 15 in the width T6 in the plan view. The same relationship holds for the other drawings.
The lower gap layer 2 is deposited on the lower shielding layer 1, and then a magnetoresistive layer 15xe2x80x2 is deposited on the entire lower gap layer 2. As shown FIG. 6A, a resist layer 20 is formed on the magnetoresistive layer 15xe2x80x2. Since the resist layer 20 is of a lift-off type, indentations 20a are formed at both bottom sides of the resist layer 20. As shown in the plan view of FIG. 6A, the resist layer 20 is formed on the entire magnetoresistive layer 15xe2x80x2 other than at two windows 20b. Thus, the magnetoresistive layer 15xe2x80x2 is exposed at the windows 20b. 
The width of the resist layer 20 between the windows 20b is set to T5. The resist layer 20 is provided to determine the width of the magnetoresistive layer 15xe2x80x2 in the track width direction, hence the width of the resist layer 20 is made substantially equal to the width T4 of the completed magnetoresistive layer 15 (refer to FIG. 5).
The regions of the magnetoresistive layer 15xe2x80x2 exposed from the resist layer 20 are removed by etching to expose the lower gap layer 2, as shown in FIG. 6B. The hard magnetic bias layers 4 and the electrode layers 5 are then formed on the exposed regions of the lower gap layer 2, as shown in FIG. 6C. A stripping solution is penetrated into the interface of the resist layer 20 and the magnetoresistive layer 15xe2x80x2 though the indentations 20a, and then the resist layer 20 is removed.
As shown in FIG. 7A, a resist layer 21 is formed on the magnetoresistive layer 15xe2x80x3 and the electrode layers 5. Since the resist layer 21 is not of a lift-off type, it has no indentations at the bottom sides. The resist layer 21 has a length L3 in the depth direction in order to define the length of the magnetoresistive layer 15xe2x80x3 in the depth direction. Thus, the length L3 of the resist layer 21 is substantially equal to the length (not shown in the drawing) of the completed magnetoresistive layer 15 shown in FIG. 5.
The exposed region of the magnetoresistive layer 15xe2x80x3 which is not covered with the resist layer 21 is removed by etching. The magnetoresistive layer 15 is thereby formed on the lower gap layer 2, and the hard magnetic bias layers 4 and the electrode layers 5 are formed on both sides of the magnetoresistive layer 15.
As described above, in the formation of the magnetoresistive layer 15, the width T4 of the magnetoresistive layer 15 in the track width is first determined by the lift-off-type resist layer 20, the hard magnetic bias layers 4 and the electrode layers 5 are formed, and then the length of the magnetoresistive layer 15 in the depth direction is determined by the resist layer 21.
The method for making the magnetoresistive layer 15, however, has the following disadvantages. In FIG. 6C, the total thickness of the hard magnetic bias layer 4 and the electrode layer 5 is larger than the thickness of the magnetoresistive layer 15xe2x80x3. Thus, as shown in FIG. 7A, the thickness h1 of the resist layer 21 on the magnetoresistive layer 15xe2x80x3 is larger than the thickness h2 on the electrode layers 5. Such a difference in the thickness causes random scattering in the exposure step due to improper focusing. As a result, the planar shape of the resist layer 21 in the transverse direction of the drawing or the track width direction is not linear as shown in the plan view of FIG. 7A, but is instead curved in the air bearing surface (ABS) direction and the depth direction, which is the reverse direction of the ABS direction.
Thus, the planar shape of the magnetoresistive layer 15 completed by etching the exposed region is also curved in the ABS face direction and the depth direction, by following the shape of the resist layer 21, as shown in FIG. 8A. Since the side in the ABS direction is polished in a subsequent step to planarize it as shown in FIG. 8B, the curvature is not substantially disadvantageous. The face in the depth direction is, however, not subjected to any treatment in the subsequent steps; hence the curved face of the magnetoresistive layer 15 in the depth direction remains.
In the step shown in FIG. 7A, the resist layer 21 is post-baked to enhance etching resistance of the resist layer 21 prior to the etching of the exposed region. The resist layer 21 is deformed by post-baking from the rectangular shape as shown in FIG. 7A to a rounded shape. A modified layer 21xe2x80x2 is formed on the resist layer 21 due to the effects of argon during ion-milling etching, as shown in FIG. 9 (a longitudinal cross-sectional view of the thin-film magnetic head having the resist layer 21). Since the modified layer 21xe2x80x2 is not removed by the resist stripping solution, it must be removed by an oxygen-plasma dry etching process.
The oxygen-plasma dry etching process, however, also etches the surfaces of the magnetoresistive layer 15 in the depth direction and the ABS direction that adjacent to the modified layer 21xe2x80x2. Thus, an indented section is formed on these surfaces. Since the surface in the depth direction is not subjected to any treatment in the subsequent steps as described above, the indented section of the magnetoresistive layer 15 in the depth direction remains, although the indented section in the ABS section is polished (see FIG. 8B).
With a narrowing trend of the track width for achieving high-density recording, the width T4 of the magnetoresistive layer 15 in the track width direction and the length in the depth direction are further decreased. Thus, the relatively large curvature and/or indentation on the surface of the magnetoresistive layer 15 in the depth direction adversely affects characteristics of the resulting thin-film magnetic head. That is, the magnetoresistive layer 15 has a multilayered structure, hence the shape and magnetic anisotropy of each sublayer of the magnetoresistive layer 15 is not stabilized, and its direct current resistance (DCR) varies at different places. These disadvantages inhibit stable reading characteristics.
Accordingly, it is an object of the present invention to provide a thin-film magnetic head having stable reading characteristics.
It is another object of the present invention to provide a method for making a thin-film magnetic head having a desired magnetoresistive layer.
A thin-film magnetic head in accordance with the present invention comprises: a nonmagnetic lower gap layer;
a nonmagnetic upper gap layer; a magnetoresistive layer; an electrode layer; and an intermediate gap layer conducting a sensing current to the magnetoresistive layer; the magnetoresistive layer and the electrode layer being formed between the lower gap layer and the upper gap layer, the intermediate gap layer being disposed between the lower gap layer and the upper gap layer; wherein the intermediate gap layer is formed in the region at both sides of the magnetoresistive layer in the track width direction and/or in the region behind the magnetoresistive layer in the depth direction.
Preferably, the thickness of the intermediate gap layer is substantially equal to the thickness of the magnetoresistive layer.
A method for making a thin-film magnetic head in accordance with the present invention comprises: a step for forming a nonmagnetic lower gap layer on a lower shielding layer; a step for forming a magnetoresistive layer on the entire surface of the lower gap layer; a step for forming a first lift-off-type resist layer on the magnetoresistive layer, and removing by etching the exposed region of the magnetoresistive layer not covered with the first lift-off-type resist layer; a step for forming an intermediate gap layer on the region, exposed by the etching step for the lower gap layer; a step for forming a second lift-off-type resist layer on the magnetoresistive layer and the intermediate layer, and removing by etching both ends of the magnetoresistive layer and the exposed region the intermediate gap layer not covered with the second lift-off-type resist layer; and a step for forming an electrode layer on the region, exposed by the etching step for the lower gap layer, and removing the second lift-off-type resist layer.
Preferably, the length of the magnetoresistive layer in the depth direction is determined by the first lift-off-type resist layer, and then the width of the magnetoresistive layer in the track width direction is determined by the second lift-off-type resist layer.
Preferably, the thickness of the intermediate gap layer is made substantially equal to the thickness of the magnetoresistive layer.
In accordance with the method of the present invention, a miniaturized magnetoresistive layer having a desired shape can be formed, hence each sublayer of the magnetoresistive layer has stabilized formal magnetic anisotropy that ensures improved reading characteristics.
According to the method of the present invention, the surface, in the depth direction, of magnetoresistive layer of the present invention is not curved.
Since the method in accordance with the present invention does not require an oxygen plasma dry etching process, the magnetoresistive layer can be produced without damage.